Membrane reactors have been proposed for numerous reactions that are thermodynamically limited such as: propane dehydrogenation to propylene, cyclohexane to benzene, ethyl benzene to styrene, steam-methane reforming to hydrogen and water-gas shift reaction to hydrogen. Most of those reactions are both reversible and endothermic. The concept of shifting thermodynamic equilibrium by removing one of the products, notably hydrogen in the case of steam-methane reformation and water-gas shift reaction, has been demonstrated to drive the reaction forward beyond its conventional thermodynamic limits thereby leading to economic and performance enhancements. Various concepts have been proposed for supplying the heat that is required for endothermic reactions. One concept is the use of heat pipes. Another concept is oxidizing part of the hydrocarbon feed in-situ by introducing an oxidant.
Membrane reactors provide a means for removing a reaction product from a reaction. Many different configurations of membrane reactors have been proposed over the years. One is a fluidized bed membrane reactor as disclosed in U.S. Pat. No. 5,326,550, Adris et al., granted Jul. 5, 1994. This patent discloses hydrogen gas being generated in a fluidized bed reactor by reacting gases namely steam and a hydrocarbon gas such as methane or natural gas in a fluidized bed of particulate catalytic material. The catalytic material is fluidized by injecting the mixture of the reacting gases at the bottom of the bed. Hydrogen generated within the bed is removed by using a selectively permeable membrane that extends through the bed and through a freeboard area above the bed. Since the reaction is endothermic, heat to maintain the bed at the desired temperature is added as required. Preferably a separator separates particulate catalytic material entrained in the gases in the freeboard area and returns the particulate material separated from the gas to the bed. The subject matter of this patent, insofar as it is relevant to the subject invention, is incorporated herein by reference.
Fluidized catalyst beds have the advantages of a high degree of solids mixing resulting in minimal temperature and concentration gradients, small particle size resulting in improved catalyst effectiveness and flexibility in shape and configuration which allows the fluidized bed to accommodate substantial permeation capacities.
U.S. Pat. No. 6,331,283 B1, Roy et al., granted Dec. 18, 2001, discloses a process of producing hydrogen by autothermal steam reformation of a hydrocarbon comprising the steps of providing a reactor vessel having a fluidized catalyst bed, introducing steam and a gaseous hydrocarbon into the vessel, introducing oxygen into the vessel, maintaining the fluidized catalyst bed temperature below the spontaneous combustion temperature of the hydrocarbon and withdrawing hydrogen from the vessel using a perm-selective membrane. The apparatus for producing hydrogen comprises a reactor vessel, steam and hydrocarbon inlets, an oxygen inlet, a fluidized bed of catalyst within the reactor vessel and a perm-selective membrane for withdrawing hydrogen from the vessel. The subject matter of this patent, so far as it is relevant to the subject invention, is incorporated herein by reference.